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AQA Biology A-Level > Biological molecules > Flashcards

Biological molecules Flashcards

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1
Q

What is an ionic bond

A

A type of bond formed through the attraction of ions with opposing charges

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2
Q

What is a covalent bond

A

A type of bond formed through the sharing of outer shell (Valence) electrons, which fills the outer shells to form a stable molecule

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3
Q

What is a hydrogen bond

A

A type of bond formed through the attraction of polar molecules with opposing dipoles

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4
Q

What is a monomer

A

A small, single, repeatable molecule that can bond to others to form a polymer

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5
Q

What are some examples of monomers

A

Nucleotides, Monosaccharides, Amino acids

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6
Q

What is a polymer

A

A large molecule made up of many similar / identical monomers bonded together

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7
Q

What are some examples of polymers

A

DNA, Polypeptides, Polysaccharides

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8
Q

How are polymers formed

A

Through a condensation reaction that bonds two or more monomers together

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9
Q

How are monomers formed

A

Through a hydrolysis reaction that breaks down / hydrolyses the polymer back into monomers

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10
Q

What is a condesation reaction

A

A reaction where the formation of the bonds in a product produces a molecule of water

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11
Q

What is a hydrolysis reaction

A

A reaction where the break down / hydrolysis of the bonds in a product requires a molecule of water

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12
Q

What are the three types of carbohydrate

A

Monosaccharides, Disaccharides, Polysaccharides

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13
Q

Which of the three types of carbohydrates are sugars

A

Monosaccharides and Diaccharides

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14
Q

Which of the three types of carbohydrates are polymers

A

Polysaccharides

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15
Q

What are the two primary uses of carbohydrates

A

Energy store and structural material for membranes and walls

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16
Q

What is the ratio of Hydrogen:Oxygen in a carbohydrate

A

2:1

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17
Q

What is the chemical formula for glucose

A

c6h12o6

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18
Q

What shaped sugar is glucose

A

Hexose

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19
Q

What are alternative forms of a hexose sugar called

A

Isomers

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20
Q

What are some isomers of glucose

A

Fructose, Galactose, Ribose

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21
Q

What is an isomer

A

A molecule with the same chemical formula but a different structural formula / lay out

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22
Q

What is a monosaccharide

A

A single sugar monomer

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23
Q

What is the general formula of a monosaccharide

A

(CH2O)n
- n can be anywhere from 3 to 7

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24
Q

How can you identify a monosaccharide by taste

A

If the sample tastes sweet

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25
Q

What are the two forms of glucose monosaccharide monomers

A

Alpha and beta

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26
Q

What is a disaccharide

A

A simple, dual sugar molecule formed through the condensation reaction of two monosaccharide monomers bonded together by a glycosidic bond

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27
Q

What is the general formula of all disaccharides

A

C11H22O11

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28
Q

How is the disaccharide maltose formed

A

Through a condensation reaction forming a C1 - 4 glycosidic bond between two molecules of alpha glucose

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29
Q

How is the disaccharide lactose formed

A

Through a condensation reaction forming a C1 - 4 glycosidic bond between one molecule of alpha glucose and one molecule of galactose

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30
Q

How is the disaccharide sucrose formed

A

Through a condensation reaction forming a C1 - 4 glycosidic bond between one molecule of alpha glucose and one molecule of fructose

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31
Q

What is the main function of monosaccharides and Disaccharides

A

To store energy

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32
Q

What is a polysaccharide

A

A large polymer comprised of many monosaccharides bonded together through glycosidic bonds formed in condensation reactions

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33
Q

Are monosaccharides and disaccharides soluble

A

Yes

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34
Q

Are polysaccharides soluble

A

No

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35
Q

Which polysaccharide is responsible for plant energy storage

A

Starch

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36
Q

Which polysaccharide is responsible for mammal energy storage

A

Glycogen

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37
Q

Which polysaccharide is responsible for structural materials

A

Cellulose

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38
Q

What are the two forms of starch

A

Amylose and Amylopectin

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39
Q

What is the structure of amylose

A

Long, unbranched, coiled chain of alpha glucose molecules bonded together by condensation reactions forming C1-4 glycosidic bonds, with a reducing end to stimulate hydrolysis

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40
Q

What is the structure of amylopectin

A

Long, highly branched, uncoiled structure of alpha glucose molecules bonded together by a mix of C1-4 and C1-6 glycosidic bonds

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41
Q

How is starch overall adapted to its functions

A
  • Compact - beneficial for storing high volumes in a small space
  • Insoluble - beneficial for not affecting water potential
  • Large - Beneficial for containment
  • Large surface area and high amount of exposed reducing ends - Beneficial for quick hydrolytic energy production
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42
Q

What is the structure of glycogen

A

Very highly branched coiled polymer comprised of many alpha glucose monomers bonded together by a combination of C1-4 and C1-6 glycosidic bonds formed in condensation reactions

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43
Q

How is glycogen different to amylopectin structurally

A
  • Higher degree of branching
  • Shorter branches (8-12 on average)
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44
Q

How is glycogen adapted for its function

A
  • Compact - beneficial for storing high volumes in a small space
  • Insoluble - beneficial for not affecting water potential
  • Large - Beneficial for containment
  • Large surface area and high amount of exposed reducing ends - Beneficial for quick hydrolytic energy production
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45
Q

What is the structure of cellulose

A

Straight chains of alternating beta glucose at 180 degrees bonded together by C1-4 glycosidic bonds formed through condensation reactions

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46
Q

Why does cellulose have alternating beta glucose molecules

A

Very high bond tension

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47
Q

How do chains of cellulose bond together to form parallel layers

A

Cross linking via hydrogen bonding

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48
Q

What is the progression of structure for cellulose polysaccharides

A

Cellulose chains -> microfibrils -> macrofibrils

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49
Q

How is cellulose adapted to its functions

A
  • Cross linking - prevents the breakdown of the polymer for energy
  • High volumes of hydrogen bonding - Increases structural rigidity and strength
50
Q

What type of molecule are lipids

A

Macromolecules

51
Q

Why are large lipid molecules not classes as polymers

A

They are not made up of
a repeating monomer

52
Q

Are lipids soluble

A

In water, no. In organic solvents (e.g., alcohols), yes

53
Q

What is the most common type of oil that makes up fats and oils

A

Triglyceride

54
Q

What is the structure of a triglyceride

A

3 fatty acid chains each bonded by an ester bond to a molecule of glycerol through condensation reactions

55
Q

What are the functions of triglycerides

A

Comprise cell membranes, insulation, energy source, waterproofing and protection

56
Q

What are the isomers of fatty acids that are found in triglycerides

A

Unsaturated (no carbon-carbon double bonds), Monounsaturated (1 carbon-carbon double bond), Polyunsaturated (more than 1 carbon-carbon double bond)

57
Q

How do double bonds affect the displayed structure of a fatty acid chain

A

Cause a kink

58
Q

Where are unsaturated fatty acid triglycerides mainly found

A

Fish, vegetable oils, nuts

59
Q

Where are saturated fatty acid triglycerides mainly found

A

Animal fats

60
Q

What is the name of the process where a triglyceride is formed

A

Esterification

61
Q

How many molecules of water are lost during one esterification reacted

A

3

62
Q

How is the structure of a triglyceride adapted to its function

A
  • Energy source - high ratio of C-H bonds
  • Low mass to energy ratio good for storage as lots of energy stored in a small
    volume
  • Large and non-polar - Insoluble so does not affect osmosis or water potential of cells
  • High ratio of H to O atoms - source of water as release water when oxidised
    (important if living in dry conditions)
62
Q

How is a phospholipid’s structure different to a triglyceride’s structure

A

2 fatty acid chains and a phosphate group bonded on the opposing side of the glycerol, each bonded by an ester bond to a molecule of glycerol through condensation reactions

63
Q

What are the functions of a phospholipid

A

Form a bilayer cell membrane

64
Q

How is the structure of a phospholipid adapted to its function

A
  • Polar molecules - form a bilayer in a aqueous environment
  • Hydrophilic heads - allow the bilayer to form and hold it in position
  • Phospholipid heads - allows formation of glycolipids
65
Q

Which section of a phospholipid is polar and why

A

The heads, the phosphate group is negatively charged

66
Q

Which section of a phospholipid is non - polar and why

A

The tails, no charged ions

67
Q

Which section of a phospholipid is hydrophilic and why

A

The head, it is polar so can therefore hydrogen bond with the water

68
Q

Which section of a phospholipid is hydrophobic and why

A

The tails, they are non-polar so can’t hydrogen bond with the water

69
Q

What is the general formula of an amino acid

A

N(H2)C(HR)C(OOH)

70
Q

How many different amino acids are there

A

20

71
Q

What is a polypeptide

A

A long chain of amino acid monomers bonded together through peptide bonds formed through condensation reactions

72
Q

Where does a peptide bond form in a di/polypeptide

A

Between the amine group (loses 1 H) and the carboxyl group (loses 1 OH), bond runs from N to C

73
Q

What are the 4 different level of protein structure

A

Primary, secondary, tertiary, quaternary

74
Q

What is the primary structure of a protein

A

The order of amino acids in the polypeptide chains.

75
Q

What determines the order of amino acids in the tertiary structure

A

The sequence of the nucleotidesin DNA

76
Q

What is the secondary protein structure

A

The way the primary protein structure is folded

77
Q

What determines the shape in the secondary protein structure

A

The location of hydrogen bonds between the amine groups and carboxyl group

78
Q

What is the main form of the secondary protein structure

A

Alpha helix

79
Q

What is the secondary form of the secondary protein structure

A

Beta pleated sheet

80
Q

How do the bonds in the secondary protein structure aid its function

A

The high abundance of hydrogen bonds keeps the alpha helix stable and reduces the risk of external mutationary effects

81
Q

What is the tertiary protein structure

A

The unique, complex, compact, 3D globular structure formed by the folding of the secondary protein structure

82
Q

Why are tertiary proteins unique

A

So they are the sole type of protein that can perform its specific function (most are enzymes)

83
Q

What are the different kinds of bonds in the tertiary protein structure

A

Disulphide (between amino acids that contain sulphur - covalent and strong), Ionic (between R-groups with positive or negative
charges - weaker than disulphide and easily broken by changes in pH),
Hydrogen (between the ‘R’ groups, are weak individually but highly abundant)

84
Q

What is the quaternary protein structure

A

How the different polypeptide chains (tertiary structures) are arranged together

85
Q

What does the tertiary structure of a fibrous protein look like

A

Long

86
Q

What are fibrous proteins use for and why

A

Structural measures, insoluble and strong

87
Q

What are globular proteins used for and why

A

Involved in cellular metabolism (e.g. enzymes; receptor proteins, protein hormones and antibodies), specific and unique tertiary structure hydrophilic / soluble

88
Q

What is the test for reducing sugars

A

Benedict’s test

89
Q

What is the test for non-reducing sugars

A

Modified benedict’s test

90
Q

What is the test for starch

A

Iodine test

91
Q

What is the test for lipids

A

Emulsion test

92
Q

What is the test for proteins

A

Biuret’s test

93
Q

How is the benedict’s test carried out

A
  • Food sample dissolved in water is mixed with
    an equal volume of Benedict’s reagent
  • Mix and heat in a water bath at 80-90◦C
  • If the solution turns orange, a reducing sugar
    is present
94
Q

How is a modified benedict’s test carried out

A
  • The sample or solution under consideration is boiled for at least fifteen minutes in hydrochloric acid (Boiling in acid breaks glycosidic bonds – the glycosidic bond is hydrolysed – This is called ACID HYDROLYSIS)
  • The solution is then neutralised by adding drops of alkali such as sodium hydrogen carbonate
  • Benedict’s test is now performed on the resulting
    solution
  • If a brick-red precipitate forms then sucrose was
    present in the original solution
95
Q

Why may a disaccharide be non-reducing

A

It can’t reduce copper (ii) ions

96
Q

How is an iodine test carried out

A
  • The sample should have iodine dropped on it, taking care not to oversaturate it
  • If the sample turns blue/black, starch is present
97
Q

How is an emulsion test carried out

A
  • Add an equal or lesser amount of alcohol to the solution
  • Shake
  • Add an equal volume of distilled water
  • If a lipid is present a cloudy white emulsion will form
98
Q

How is a biuret’s test carried out

A
  • Add equal volumes of copper sulphate and sodium hydroxide to
    the solution
  • If a protein is present, it will turn violet.
99
Q

What is an enzyme

A

A globular protein that acts as a biological catalyst with a unique and specific tertiary structure and active site that bonds with a specific substrate to form an enzyme substrate complex, which lowers the activation energy needed for a chemical reaction

100
Q

How is the shape of an enzyme adapted to its function

A
  • Specific 3D tertiary structure
  • Substrate complementary shape to active site
  • Substrate can bind to active site
101
Q

What are the two models of how an enzyme works

A

Lock and key, induced fit

102
Q

What is the lock and key theory

A
  • The enzymes’ active site is a specific shape due to its tertiary structure.
  • The substrate has a complementary shape to the active site, and it fits in like a key fitting into a lock
  • Temporary structure called the enzyme-substrate complex formed
  • Products have a different shape from the substrate
103
Q

What is the induced fit model

A
  • The enzyme’s active site is not exactly the same shape as the substrate
  • Active site moulds itself around the substrate as the enzyme substrate complex is formed
  • This explains why enzymes that can react with a range of substrates of similar types
104
Q

How is gradient calculated on a rate of reaction graph

A

rise / run

105
Q

What factors can affect the rate of enzyme catalysed reactions

A

Temperature, pH, Enzyme concentration, Substrate concentration, Inhibitors

106
Q

How does temperature affect the rate of enzyme catalysed reactions

A
  • As the temperature increases the Kinetic Energy of the molecules increases.
  • They move about more quickly and collide more so frequency of successful
    collisions increases.
  • The reaction goes faster until the optimum temperature
  • Above the optimum temperature hydrogen bonds holding the enzyme’s tertiary structure in place start to break.
  • The active site shape changes shape and can’t bind the substrate so less enzyme substrate complexes
  • The enzyme is denatured & the reaction slows
107
Q

How does pH affect the rate of enzyme catalysed reactions

A
  • The change in H+ affects the charge on the amino acid
  • This causes (ionic) bonds in the tertiary structure to break
  • This alters the tertiary structure distorting the active site shape
  • Substrate can no longer bind so no enzyme substrate complexes are
    formed
108
Q

What is pH

A

The measure of the concentration of hydrogen ions in a solution

109
Q

How can a small change in pH affect an enzyme catalysed reaction

A

A small change in pH can affect the charge on the amino acids that make up the active site thereby changing the shape of the active site so the substrate can no longer fit into to bind to it

110
Q

How can a large change in pH affect an enzyme catalysed reaction

A

A large change in pH breaks ionic bonds in the enzyme structure. The tertiary structure breaks, changing the enzyme’s shape. The active site changes shape and the substrate can no longer fit into to bind to it

111
Q

How can substrate concentration affect an enzyme catalysed reaction

A

The increasing amount of substrate can bind to
active sites on the enzymes as more successful
collisions occur. At this point, the amount of substrate is limiting because as the rate is increasing as the
concentration of substrate also increases. Once every enzyme active site is occupied, adding more substrate makes no difference. At this point, the concentration of substrate is no longer limiting, something else is

112
Q

What are enzyme inhibitors

A

Substances that directly or
indirectly interfere with the functioning of the active
site of an enzyme

113
Q

What are the two types of enzyme inhibitors

A

Competitive and non-competitive

114
Q

How does competitive inhibition work

A

A competitive inhibitor molecule has a similar
structure to the normal substrate molecule, and it
can fit into the active site of the enzyme. The inhibitor is not permanently bound to the active site. When it leaves another molecule takes its place

115
Q

In what situation does the competitive inhibitor successfully compete for the active sites

A

When substrate concentration is low

116
Q

Can competitive inhibition be overcome

A
  • Yes, the effect of the competitive inhibitor is overcome when the high concentration of substrate molecules competes
    successfully for the active sites of the enzymes
  • At high substrate concentration, maximum reaction rate is achieved
117
Q

How do non-competitive inhibitors work

A
  • A non-competitive inhibitor molecule has a different
    structure from the substrate molecule
  • It binds to another part of the enzyme molecule causing the shape of the whole enzyme to change, so the active site changes and it can no longer bind substrate molecules.
118
Q

Can non-competitive inhibition be overcome

A
  • No, high substrate concentration has no effect because the molecules are
    not competing for the same binding site
  • Maximum rate of reaction not
    reached
119
Q

How does potassium cyanide act as an inhibitor poison

A
  • Inhibits a vital respiratory enzyme called cytochrome oxidase (found inside
    mitochondria)
  • Cytochrome oxidase normally combines oxygen and hydrogen together to form water and allows ATP creation.
  • Cyanide non-competitively inhibits chytochrome
    oxidase changing the shape of its active site meaning no ATP creation.
  • ## Any reactions requiring ATP are no longer supplied. The body eventually has no energy supply causing total cell failure
120
Q

How does the fasciculation protein in snake venom act as an inhibitor poison

A
  • Inhibits Acetylcholinesterase which is an enzyme used to degrade a neurotransmitter called Acetylcholine
  • Fasciculation acts as a competitive inhibitor preventing the acetylcholine from being broken down by
    Acetylcholinesterase after an impulse transmission.
  • In skeletal muscle fasciculations stop nerve impulses from being transmitted and hence stop muscle contraction.
  • Eventually this will lead to flaccid paralysis.
121
Q

How do HIV Protease inhibitors act as medical inhibitors

A
  • Competitively inhibits HIV virus protease enzymes.
    Normally the virus uses this to cut viral RNA into smaller pieces so as into implant genes into the host cells DNA and hence replicate
  • The inhibitor binds specifically with the HIV protease enzymes active site preventing longer viral RNA pieces from bindings, as a result the RNA is not cut into smaller pieces so it cannot be implanted into the host cells DNA = no replication
  • A host cell can be infected by HIV but it cannot be ‘hijacked’ into making more HIV copies as a result of DNA implantation by the
    virus

AQA Biology A-Level (1 decks)

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